In Marxism, bourgeois nationalism is the practice by the ruling classes of deliberately dividing people by nationality, race, ethnicity, or religion, so as to distract them from initiating class warfare. It is seen as a divide and conquer strategy used by the ruling classes to prevent the working class from uniting against them (hence the Marxist slogan, Workers of all countries, unite!).
After the October Revolution, the Bolshevik government based its nationalities policy (korenization) on the principles of Marxism. According to these principles, all nations should disappear with time, and nationalism was considered a bourgeois ideology.
In his Report on the 50th anniversary of the formation of the USSR, Leonid Brezhnev emphasized: "That is why Communists and all fighters for socialism believe that the main aspect of the national question is unification of the working people, regardless of their national origin, in the common battle against every type of oppression, and for a new social system which rules out exploitation of the working people."
Bourgeois nationalism as a concept was discussed by China's president, Liu Shaoqi as follows:
The exploitation of wage labour, competition, the squeezing out, suppressing and swallowing of rivals among the capitalists themselves, the resorting to war and even world war, the utilisation of all means to secure a monopoly position in its own country and throughout the world - such is the inherent character of the profit-seeking bourgeoisie. This is the class basis of bourgeois nationalism and of all bourgeois ideologies. [...] The most vicious manifestations of the development of bourgeois nationalism include the enslavement of the colonial and semi-colonial countries by the imperialist powers, the First World War, the aggression of Hitler and Mussolini and the Japanese warlords during the Second World War, and the schemes for the enslavement of the whole world undertaken by the international imperialist camp, headed by American imperialism.